The present invention relates to a planar light source unit for emitting a linear light beam, which unit is used in a display having a backlight device.
In recent years, the liquid crystal display device having the backlight device is used in the notebook personal computer, desktop personal computer, and others.
FIG. 10 is a perspective view showing a conventional planar light source unit, and FIG. 11 is a sectional side view. In the drawings, reference numeral 10 designates a planar light source unit which comprises a transparent light leading plate 1 made of plastic and formed into a rectangular parallelepiped, and a plurality of LEDs 2 linearly mounted on a print substrate (not shown). The light leading member 1 has a light discharge surface 1a and a light diffusing plane 1b. On the light diffusing plane 1b, a plurality of embossed grooves or embossed dots 1c are formed, so that light is reflected from the diffusing plane 1b to the light discharge surface 1a.
On the light diffusing plane 1b, a reflection plate 3 made of a white plastic sheet is attached so as to reflect the light passing through the light diffusing plate 1b.
The light discharged from the light discharge surface 1a irradiates a liquid crystal display panel 7 from the back of the panel.
By adjusting the density of the embossed wrinkle or dots 1c, or by changing the shape of the dot 1c, it is possible to somewhat equally irradiate the liquid crystal display panel 7. In order to equally irradiate the panel, the number of the LEDs 2 must be increased. However, the increase of the number of the LEDs causes the manufacturing cost, the size of the unit, and power consumption to increase.